Paul seems to be very careful at the beginning of I Corinthians 7 in his statements, hedging them so that they are not taken as absolutes, e.g. vv. 1-2 and 8-9 with "it is good [...] but", and v.6 with "by way of concession, not of command", and in the middle of the chapter when he's talking about divorce he does clearly separate his "I say, not the Lord" (v. 12) from what "not I, but the Lord" says (v. 10). So while he is giving both advice and doctrine together, overall he wants his readers to know which is which.
He seems to want to make it clear that yes, while he does prefer people to live an unmarried life, he also realizes that a lot of people can't pull that off (vv. 1-2, v. 8, NASB quoted):
It is good for a man not to touch a woman. But because of immoralities, each man is to have his own wife, and each woman is to have her own husband.
I say to the unmarried and to widows that it is good for them if they remain even as I. But if they do not have self-control, let them marry; for it is better to marry than to burn with passion.
But he also wants to say that the choice between celibacy and marriage is not between right and wrong, but between the best thing and the next best thing (v. 38):
So then both he who gives his own virgin daughter in marriage does well, and he who does not give her in marriage will do better.
He gives two reasons for preferring the celibate life; the first (v. 26) seems to be based on the context of his time:
I think then that this is good in view of the present [or impending] distress, that it is good for a man to remain as he is.
(He does not elaborate on what the impending distress is; presumably the Corinthians understood what he meant.) His other reason is that of religious devotion (vv. 32-35):
One who is unmarried is concerned about the things of the Lord, how he may please the Lord; but one who is married is concerned about the things of the world, how he may please his wife, and his interests are divided. The woman who is unmarried, and the virgin, is concerned about the things of the Lord, that she may be holy both in body and spirit; but one who is married is concerned about the things of the world, how she may please her husband. This I say for your own benefit; not to put a restraint upon you, but to promote what is appropriate and to secure undistracted devotion to the Lord.
This seems to be an elaboration of his statement in v. 3 that "The husband must fulfill his duty to his wife, and likewise also the wife to her husband." To this reasoning we may also adduce Jesus' statement in Matthew 6:24:
No one can serve two masters; for either he will hate the one and love the other, or he will be devoted to one and despise the other.
If Christians marry, then, they are either going to have a less perfect devotion to God (due to attending to their spouses) or a less perfect devotion to their spouses (due to attending to God). Paul does not want his Christians to think of marriage as an expected or necessary part of life--something one would just expect to do when one grows up, like getting a job--but as something to be entered into thoughtfully and with understanding of the consequences on one's relationship to God.